The oil-in-water-in-oil type emulsified composition obtained by further emulsifying and dispersing an oil-in-water type emulsified composition (hereafter referred to as O/W type emulsion) in the oil phase is called an O/W/O type multiple emulsion and has become important in various industrial applications such as cosmetics, food, and medicines.
That is, while a usual O/W type emulsion is obtained by simply dispersing the oil phase in the water phase, the particle structure of an O/W/O type multiple emulsion comprises an inner phase oil 14 dispersed in a water phase 12 dispersed in an outer phase 10, as shown in FIG. 1.
Because of this, a special touch during use can be achieved which cannot be obtained by a simple O/W type or W/O type emulsion.
As a means to obtain a stable multiple emulsion, Japanese unexamined patent publication Tokkai Hei 8-323188, for example, describes a process in which a hydrophilic nonionic surfactant is used to prepare the O/W type fine emulsion which is to be the inner phase, and this O/W type emulsion is dispersed and emulsified in the oil based ingredient containing an organophilic modified clay mineral which is to be the outer phase oil. The multiple emulsion obtained with this preparation method is known to suppress the merging of the inner phase oil and the outer phase oil and have significantly increased stability over time.
However, although solid and/or semi-solid oil ingredients such as higher alcohols and waxes are blended in to improve the skin-compatibility of a cream, in the case of the aforementioned O/W/O type multiple emulsion which contains the organophilic modified clay minerals in its outer phase oil, there is a problem in that blending these solid and/or semi-solid oil ingredients in the outer phase oil or the inner O/W type emulsion emulsified by using a nonionic surfactant degrades the stability over time.
Based on the aforementioned consideration, the inventors conducted earnest research to obtain a stable O/W/O type multiple emulsion and discovered that solid or semi-solid oil ingredients can be blended in the inner phase O/W type emulsion in a stable manner and an O/W/O type multiple emulsion with superior stability over time and improved skin-compatibility of the base into the skin can be obtained by adding an amphiphilic substance and surfactant of a specific combination to the O/W type emulsion, adding an organophilic modified clay mineral and an emulsifying agent with a HLB of 7 or less to the outer phase oil, and then dispersing the O/W type emulsion in the outer phase oil at a specific weight ratio, thus completing the present invention.
Also, based on the aforementioned consideration, the inventors conducted earnest research to obtain a stable O/W/O type multiple emulsion and discovered that solid or semi-solid oil ingredients can be blended in the inner phase O/W type emulsion in a stable manner and an O/W/O type multiple emulsion with superior stability over time and improved skin-compatibility of the base into the skin can be obtained by adding an amphiphilic substance and N-long chain acyl acidic amino acid monosalt of a specific combination to the O/W type emulsion, adding an organophilic modified clay mineral and an emulsifying agent with a HLB of 7 or less to the outer phase oil, and then dispersing the O/W type emulsion in the outer phase oil at a specific weight ratio, thus completing the present invention.
The object of the present invention is to provide an O/W/O type multiple emulsion which exhibits superior stability over time even when a solid or semi-solid ingredient is added to improve the usability and dies not limit the selection of the oil ingredient to be contained in the O/W type emulsion which is to be the inner phase.